Re: [tsvwg] ECN encapsulation draft - proposed resolution

["De Schepper, Koen (Nokia - BE/Antwerp)" <[e-mail]>]

Not having followed the full discussion/history, for me preserving the probability of marks is important (whether on bytes or packets), and as marking/dropping is usually applied in the network according to a probability in a closed control loop, it is probably the best way forward. Even if marking is applied by time distance and/or number of bytes or a count algorithm, it will converge to the "right" probability. This means any reassembly that preserves the average probability is good enough. Due to multiple bottlenecks and RTT dependencies, marking/dropping probability to rate/throughput is not an exact science anyway (though we should try to approach this as much as possible in a reasonable way).

So for me following simple algorithms would be ok to use:
- only mark if the first (even partial) segment of the reassembled packet is marked (ignore marks on any other segments)
- apply a random probability on the packet based on the ratio of marked bytes in the packet and full packet size

I believe both algorithms keep both byte and packet probability equal. It might not fulfil the immediate requirement, but since an AQM applying a low probability is not an immediate action anyway, it is not so important. An immediate AQM like the step threshold is marking with a high marking probability (100%) a series of packets, which is then also immediately carried forward during decapsulation by both algorithms.

Koen.


-----Original Message-----
From: tsvwg <[e-mail]> On Behalf Of Jonathan Morton
Sent: Sunday, June 6, 2021 5:02 AM
To: Bob Briscoe <[e-mail]>
Cc: [e-mail]; Markku Kojo <[e-mail]>
Subject: Re: [tsvwg] ECN encapsulation draft - proposed resolution

> On 6 Jun, 2021, at 2:06 am, Bob Briscoe <[e-mail]> wrote:
> 
> Before we do, can we make sure we're all on the same page regarding some basics that I believe are /facts/ about preserving markings when PDU boundaries change. Do you agree with the following table that I asked about earlier:
> 
>                   | marked    marked
>                   | PDUs      bytes
> -------------------+------------------
> preserving prop'n  |  ==        ==
> preserving number  |  !=        ==
> 
> 
> IOW, do you agree that the three that are tagged as '==' are equivalent ways of expressing the same thing, but different from the one tagged '!=' ?

This question just tells me that you are still focusing on the wrong metrics.  The number and/or proportion of marked bytes is IRRELEVANT.  What matters are the number of bytes and/or time interval BETWEEN marks.

I explained this in more detail in my previous post.

 - Jonathan Morton